Report of Results for Sampling and Pump-Testing
of Monitoring Wells 4s and 4i at Lemon Lane Landfill
February 7, 2002
Pump Test PCB Results [PDF]
Scope of Work
1.0 Background
Sampling and pump testing of monitoring wells 4s and 4i was conducted on
February 7, 2002 at Lemon Lane Landfill. These tests were conceived on the
basis of questions generated from dye and pump testing conducted in November
2001. The testing was conducted according to the Scope of Work documents
attached in Appendix 1 of this report.
1.1 Well 4s
Previous PCB levels in well 4s have been relatively low, based on low volume
purge rates. However, the base flow potentiometric measurements have
consistently shown 4s is a low point. During the natural gradient tracer test of
November 2001, well 4s received a relatively high detection of fluorescein, albeit
in one isolated sample. Well 4s is screened at 804.5 to 817.5' elevation, which is
above the high-water producing anastomotic zone at the 795-800' elevation. The
goals of this test were:
- Determine if high levels of PCBs exist near the well
- Determine the short term water production rate
- Determine if pumping 4s would induce drawdown in other wells
1.2 Well 4i
PCB levels in well 4i prior to the 2000 removal and capping operation have been
relatively low, with one exception. In 1995 the lower portion of the well was
plugged with bentonite to prevent possible cross-contamination. In July 2001,
testing revealed high levels of PCBs in the well. Drawdown levels in that test
were also high, on the order of 3-5 feet. Later testing on the first of August still
showed high PCBs and drawdown of 4-5'. In later August part of that bentonite
plug was removed in order to conduct cross-hole seismic tomography. When 4i
was sampled and pumped on November 6, PCB levels were 1-2 ppb. The
suspicion is that bentonite was plugging the 795-800' zone and the high PCBs
and high drawdown were due to pumping from a higher zone.
During the November 2001 pump tests it was noticed that some wells screened
above the 795-800' zone would drawdown while that zone was being pumped. It
was not known which shallow wells might respond. Presumably, shallow wells
that respond to pumping of the 795-800' zone would reflect phreatic
potentiometric levels, while shallow wells that did not respond might reflect
vadose water levels.
The goals of the test, then, were:
- Determine if drawdown, and by implication, transmissivity of the well had
changed from the summer 2001 data
- Determine if significant PCB levels exist near the well
- Determine which shallow wells respond to pumping
2.0 Sampling and Pumping
2.1 Well 4s
Attached in Appendix 2 are the field data sheets for the 4s test. The initial
pumping rate at well 4s was 3.3 gpm. Initial PCB samples were taken, but before
a sample could be taken at 15 minutes, the well went dry at 14 minutes. This is
noted as Test A. Approximately 45 gallons of water had been pumped. The well
recovered to its initial level within 5 minutes, and a sample was pulled. The
pump was restarted again at 0.8 gpm and at 15 minutes was increased to 2.0
gpm. The well appeared to be able to sustain this rate. Pumping was continued
for 60 minutes and this is noted as Test B. Approximately 130 gallons was
pumped during this test. Samples for PCBs and TSS were taken at the 15, 30,
45, and 60 minute intervals. The results for the PCB and TSS analyses, along
with their associated field parameters are show in Table 1. Total drawdown in
the pumping well as measured by hand is shown on Figure 1. Attached in
Appendix 3 are the laboratory certificates of analysis. Figures 2, 3, and 4 are the
plots of the data from the dataloggers that were logging water levels at 5 minute .
intervals in wells MW-21, MOO-6 and NN-300a, respectively.
2.2 Well4i
Attached in Appendix 4 are the field data sheets for the 4i test. The pumping rate
at well 4i was sustained at 10.5 gpm. Initial PCB samples were taken. Pumping
was continued for 70 minutes. Approximately 735 gallons was pumped from this
test. Samples for PCBs and TSS were taken at the 15, 30, 45, and 60 minute
intervals. The results for the PCB and TSS analyses, along with their associated
held parameters are show in Table 1. Total drawdown in the pumping well as
measured by hand is shown on Figure 5. Attached in Appendix 5 are the
laboratory certificates of analysis.
3.0 Results and Discussion
3.1 Well 4s
Well 4s is screened and/or open to the formation between about 804.5' and
817.5' elevation amsl. This segment of the formation does not appear to be a
high water producing zone, as evidenced by the well going dry at a 3.3 gpm
pumping rate. However, it is quite amazing that at the low pumping rate of 2 gpm
for just an hour, that drawdown was induced in shallow well NN-300a, 525 feet
away. Well NN-300a is open to the formation from top of bedrock (857.51') to
bottom of the boring at elevation 809.8'. It seems apparent that pumping well 4s
is similar to pumping the other phreatic wells and those water levels in 4s and
NN-300a likely represent phreatic conditions. However, consideration must be
given to the possibility that there is drilling-induced cross-connection. That is,
drilling of MW-20 and MW-21 nearby 4s and 4i may have created cross-
connections between the wells so that pumping from 4s is drawing water from
the anastomotic zone via MW-21. Nevertheless, there still seems to exist a low
flow phreatic gradient from MW-20 to MW-4i to MW-21 to 4s.
Table 1 lists the results for the PCB samples taken during the pump test. Test A
is the higher pumping rate of 3.3 gpm, where the well was pumped dry in 14
minutes. The 5-minute sample was higher than the first sample at the start of
pumping, but the sample pulled immediately after the well recovered was only
2.2 ppb. PCBs remained at relatively low levels during the 60 minutes the well
was pumped at the lower rate (Test B).
The goals of the test were met in that:
- It does not appear there are high PCBs near well 4s.
- The short term production rate is less than 3.3 gpm.
- Drawdown can be induced in other wells by pumping 4s.
3.2 Well 4i
Maximum drawdown produced in well 4i during the pump test was 1.02 feet once
the level stabilized. This indicates that there was a change in hydraulic
conditions from the summer pump test. The anastomotic zone was likely
plugged with bentonite during the summer tests. This may mean that the high
PCB pulse that was detected in those tests was moving in an upper zone other
than the 795-800' anastomotic zone.
Table 1 shows the results of the PCB sampling. Although the first sample was
15 ppb, levels declined to a few ppb after 30 minutes. These are typical PCB
results obtained from pumping the anastomotic zone and confirm the hydraulic
conditions in this well changed from the summer pump test.
Drawdown was induced in shallow wells NN-12a, 00-125a, NN-300a, and OO-
587a. This indicates that their low flow water levels represent phreatic
conditions. No drawdown was apparent in wells MW-1s and 00-300a, indicating
that their levels represent vadose conditions.
The goals of the test were met in that:
- It was determined that well hydraulics had changed from summer 2001.
- High levels of PCBs do not seem to exist near the well, at least from the
zone it is currently drawing water from.
- Of the shallow wells tested, MW-1s and 00-300a did not respond to
pumping.
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